1. Field of the Invention
The present invention relates to a polyamide containing polymer mixture having a specific property profile and comprising a polyamide, a high density polyolefin onto at least part of which an unsaturated carboxylic acid or an unsaturated carboxylic acid derivative has been grafted, and a grafted polyolefin elastomer containing, among others, ethylene and propylene as monomer units, and wherein the mixture has a melt viscosity of from about 1,000 to about 1,400 Pa.multidot.s at 270.degree. C. and under a load of 122.6 N. The invention further relates to the use of this mixture for the production of shaped objects, particularly by injection molding, extrusion, co-extrusion, blow molding or reshaping. The present invention further relates to a blow molded shaped bag comprising the above mixture, and useful as the inner layer of a container comprising an outer layer and an inner layer with a propellant disposed therebetween as well as a valve, and to a container containing such a molded shaped bag.
2. Technology Background
U.S. Pat. No. 3,373,222 claims a blend of polyolefin and polyamide including a special carboxylized polyethylene as compatibility enhancer. The drawback here is the relatively low effectiveness of the compatibility enhancer which results in poor mechanical properties. The barrier characteristics of such a blend are also poor.
DE 2,722,270.A discloses a binary mixture having a high melt viscosity of polyamide and modified polyethylene, with the mole equivalents of their active groups having to meet a specific stoichiometry in order to be able to solve the respective problem, namely to increase impact strength.
U.S. Pat. No. 4,410,482 discloses a special process for producing a shaped object in which two-dimensional, parallel extending mutually overlapping layers of a polycondensate are present in a polyolefin matrix. This very special structure is intended to improve the mechanical properties as well as the barrier properties.
DE 4,029,964.A1 claims a large-size container composed of a laminate of two to three layers, with one layer being formed of a modified polyamide in the form of a binary blend of polyamide and a grafted polyolefin, while the remaining layers are constructed of a grafted polyethylene. The drawback is the high rigidity of this laminate, since multi-layer structures reduce flexibility.
DE 4,010,958.A1 discloses a stretched, shrinkable tubular sheet of a binary blend of polyamide and acid-modified polyolefin for the production of a sausage skin which has an improved barrier effect and an improved delamination behavior. The drawback is here that a copolyolefin containing an .alpha.,.beta.-unsaturated carboxylic acid as the comonomer must be employed as the compatibility enhancer.
U.S. Pat. No. 4,346,194 discloses a blend of nylon 6, nylon 6,6 and grafted EPDM having an improved impact strength at low temperatures. This blend exhibits only limited effectiveness as a barrier material. Moreover, due to the double bonds in the EPDM, its stability against heat and/or light influences is low.
EP 0,397,531.A1 claims a binary blend of an aromatic polyamide and a grafted polyolefin which must have a specific degree of crystallinity and a specific glass transition temperature. Such a blend permits the production of very rigid shaped bodies having a high resistance to deformation due to heat.
EP 0,519,248.A1 describes thermoplastic molding materials on a basis of partly aromatic copolyamides and polyolefins that are distinguished by good impact strength and increased processing stability. The polypropylene used as component (B) is very rigid and exhibits a tension-E module of approximately 1800 N/mm.sup.2. It additionally has poor barrier characteristics in comparison to hydrocarbons such as HD polyethylene. Bonding agents such as Polybond.RTM., Hostamont.RTM., Admer.RTM., etc. are used as component (C) in EP 0,519,248.A1. EP or EPDM, which are very sensitive to the effects of heat and light because of the included double bonds, are used as caoutchoucs to increase the impact strengths of the described polyamides. The melt viscosity of the formulation is too high for these to be used in the production of special molded objects.
The objective of DE 4,131,908.A1 is to make available formulations having the lowest possible melt viscosity and the highest possible E module for molded parts with improved homogeneity. A melt index of less than 1.5 g/10 min. when measured at 190.degree. C., 2.16 kg, is desired; this corresponds to a capillary melt viscosity of&gt;100 Pa.multidot.s at 285.degree. C. and 1000 s.sup.-1. The acid-modified olefin has a melt index between 50 and 150 g/10 min. when measured at 190.degree. C., 2.16 kg. In particular, the modified polyethylene has a melt index of less than 5 g/10 min. when measured at 290.degree. C., 2.6 kg. Thus, the polypropylene used in this instance is again too rigid. EPDM, which is very sensitive to the effect of heat and/or light because of the contained double bonds, is used as an impact-strength modifier.
EP 0,346,148.A2 is intended to create a polyamide mixture with improved low-temperature viscosity, good flow and good adherence to a surface coating. The polyethylene used in this instance has low viscosity and a melt index from 1 to 30 g/10 min. (190.degree. C.). The polypropylene is rigid and exhibits a low impact value. Again, EPDM caoutchouc is used as an impact-strength modifier. Table 1 of this document shows that high rigidity is desired.
EP 0,261,748.A2 describes a new impact-strength modifier, namely a special block copolymer, and a method for producing it. The block copolymer containing styrene has a poor barrier effect against water. The poly-.alpha.-olefin used is characterized by a melt viscosity of approximately 100 to 5000 cp. (1 to 50 Pa.multidot.s).
EP 0,337,153.A2 describes polyamide blends for fuel lines in automobiles. These lines should possess the following properties: low-temperature impact strength, salt resistance and barrier characteristics against gasoline and alcohol. Also in this case, EPDM and LD-EP are used, which have poor barrier characteristics. The blends in EP 0,337,153 have a very high melt viscosity.
The materials described in EP 0,519,248.A1, DE 4,131,908.A1, EP 337,153.A2 and EP 0,261,748.A2 are intended for different requirement profiles; in most cases, a very rigid product is desired. The melt viscosities are either very low or too high.
It has therefore been an object of the present invention to make available a polymer mixture having a very specific property profile which will ensure the optimum balance between mechanical characteristics and barrier effect. This property profile includes the following requirements:
* high flexibility without prior conditioning steps; PA0 * good impact strength at room temperature; PA0 * high barrier effect against solvents, particularly water, alcohols and alkanes; PA0 * meeting the high demands of a blow molding process; PA0 * good workability and machinability; PA0 * employing an easily engineered and economical process for imparting compatibility. PA0 (A) 50 to 75 parts by weight of polyamide 6, polyamide 6,6, polyamide 12 or mixtures thereof; PA0 (B) 15 to 30 parts by weight of a polyolefin onto which an unsaturated carboxylic acid or an unsaturated carboxylic acid derivative has been grafted and which has a density from about 0.921 to about 0.96 g/cm.sup.3, the extent of grafting being between about 0.01 and about 1 weight percent with respect to the total weight of grafted and non-grafted polyolefin; PA0 (C) 10 to 20 parts by weight of a grafted polyolefin elastomer which includes, among others, ethylene and propylene units, and PA0 (D) additives selected from the group consisting of stabilizers, anti-friction agents and fillers,
In addition, as a special use, a blow molded component produced from this mixture is to be a component of a special container in which a propellant is unable to escape together with the useful product.
These objectives are accomplished by the polyamide-containing polymer mixture according to the invention.